1 Ionic and covalent Bonding

2.2.2 Bonding and Structure Metal atoms lose electrons to form +ve ions. Non-metal atoms gain electrons to form -ve ions. Mg goes from 1s2 2s2 2p63s2 to Mg2+ 1s2 2s2 2p6 O goes from 1s2 2s2 2p4 to O2- 1s2 2s2 2p6 Ionic bonding is stronger and the melting points higher when the ions are smaller and/ or have higher charges. E.g. MgO has a higher melting point than NaCl as the ions involved (Mg2+ & O2- are smaller and have higher charges than those in NaCl , Na+ & Cl- ) Ionic Bonding The ions in an ionic solid are arranged in a regular 3D pattern called a giant ionic lattice Na+ ClThe sticks in this diagram are there to help show the arrangements of the ions. They do not represent the ionic bonds. Ionic bonding is between ions and all their surrounding oppositely charged ions. Each sodium ion in this structure is surrounded and equally attracted by six chloride ions. The ionic bond is the attraction between all these ions •High melting points – There are strong electrostatic attractive forces between the oppositely charged ions in the lattice •Non conductor of electricity when solid- The ions are held together tightly in the lattice and can not move so no charge is conducted •Good conductor of electricity when in solution or molten – The ions are free to move when in solution and molten. Charge can be carried Typical Physical properties of Ionic Compounds • They are usually soluble in aqueous solvents.Definition: An Ionic bond is the electrostatic force of attraction between oppositely charged ions formed by electron transfer.Covalent Bonding Definition: covalent bond is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms A Dative covalent bond forms when the shared pair of electrons in the covalent bond come from only one of the bonding atoms. A dative covalent bond is also called co-ordinate bonding. Common examples you should be able to draw that contain dative covalent bond (e.g. NH4+ , H3O+ , NH3BF3 ) O H H H + .. N H H H B Cl Cl Cl The direction of the arrow goes from the atom that is providing the lone pair to the atom that is deficient Dative Covalent bonding The dative covalent bond acts like an ordinary covalent bond when thinking about shape so in NH4+ the shape is tetrahedral The term average bond enthalpy is used as a measurement of covalent bond strength. The larger the value of the average bond enthalpy, the stronger the covalent bond. Bonding Structure Examples Ionic : electrostatic force of attraction between oppositely charged ions Sodium chloride Magnesium oxide Covalent : shared pair of electrons Simple molecular: With intermolecular forces (Induced dipole–dipole, permanent dipole-dipole, hydrogen bonds) between molecules Iodine Ice Carbon dioxide Water Methane Giant Ionic Lattice Bonding and Structure. Only use the words molecules and intermolecular forces when talking about simple molecular substances Property Giant Ionic Molecular (simple) boiling and melting points high- because of giant lattice of ions with strong electrostatic forces between oppositely charged ions. low- because of weak intermolecular forces between molecules (specify type e.g Induced dipole–dipole/hydrogen bond) Solubility in water Generally good generally poor conductivity when solid poor: ions can’t move/ fixed in lattice poor: no ions to conduct and electrons are localised (fixed in place) conductivity when molten good: ions can move poor: no ions general description crystalline solids mostly gases and liquids